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Light-scattering measurements have enabled us to determine that the transition to sonoluminescence is characterized by a bifurcation in the dynamics of a trapped pulsating bubble. These experiments also reveal that in the sonoluminescence (SL) state, changes in bubble radius of only 20% are associated with factors of 200 in the intensity of emitted light. This sensitivity of SL suggests that it originates from the kind of singular behavior that arises from the implosion of a shock wave. Theoretical extrapolations of this model to energy scales for fusion are discussed.PACS numbers: 78.60. Mq, 42.65.Re, 43.25.+y, 47.40.Nm The radiation pressure of a resonant sound field in a liquid can trap a small gas bubble at a velocity node [1].At a sufltciently high sound intensity the pulsations of the bubble are large enough to prevent its contents from dissolving in the surrounding liquid [2,3]. For an air bubble in water, a still further increase in intensity causes these pulsations to become so enormous and nonlinear that the supersonic [4] inward collapse of the bubble concentrates the acoustic energy by over 12 orders of magnitude [5] so as to emit picosecond flashes [6] of broadband light which extend well into the ultraviolet [7] and which furthermore are synchronous [8] with the sound field to picosecond accuracy.We now use light scattering techniques to determine the dependence of the light emitting mechanism on the bubble dynamics. In particular we find that the transition to sonoluminescence (SL) involves a sudden decrease in the bubble's size. In the SL state changes in experimental parameters which vary the bubble radius by 20% cause a hundredfold increase in light emission. Measurements of the bubble's dynamic susceptibility suggest that while the parameter spacer for SL is sharply delineated, the establishment of a steady state involves long time scales on the order of seconds. Our calculations suggest that this extremely sensitive dependence of sonoluminescence on bubble dynamics originates from the singularity which forms when a shock wave implodes [9]. Idealized theoretical extrapolations indicate that as the shock radius passes through 60 A the temperatures and densities are high enough for fusion.The extreme sensitivity of SL to external parameters such as the water temperature and the sound field amplitude, is indicated in Fig. 1 which shows that, as the water temperature decreases from 40 C to 1 C, the intensity of the light emission increases by a factor of over 200.

The "physics of complexity" in space plasmas is the central theme of this exposition.It is demonstrated that the sporadic and localized interactions of magnetic coherent structures arising from the piasma resonances can be the source for the coexistence of nonpropagating spatiotemporal fluctuations and propagating modes. Non-Gaussian probability distribution functions of the intermittent fluctuations from direct numerical simulations are obtained and discussed. Power spectra and local intermittency measures using the wavelet analyses are presented to display the spottiness of the small-scale turbulent fluctuations and the non-uniformity of coarse-grained dissipation that can lead to magnetic topological reconfigurations. The technique of the dynamic renormalization group is applied to the study of the scaling properties of such type of multiscale fluctuations. Charged particle interactions with both the propagating and nonpropagating portions of the intermittent turbulence are also described. 7https://ntrs.nasa.gov/search.jsp?R=20040084709 2018-05-10T23:11:02+00:00Z

We report measurements of the vacuum ultraviolet (VUV) emission spectra of a microwave-discharge hydrogenflow lamp (MDHL), a common tool in astrochemistry laboratories working on ice VUV photoprocessing. The MDHL provides hydrogen Ly-α (121.6 nm) and H 2 molecular emission in the 110-180 nm range. We show that the spectral characteristics of the VUV light emitted in this range, in particular the relative proportion of Ly-α to molecular emission bands, strongly depend on the pressure of H 2 inside the lamp, the lamp geometry (F type versus T type), the gas used (pure H 2 versus H 2 seeded in He), and the optical properties of the window used (MgF 2 versus CaF 2). These different configurations are used to study the VUV irradiation of CO ice at 14 K. In contrast to the majority of studies dedicated to the VUV irradiation of astrophysical ice analogs, which have not taken into consideration the emission spectrum of the MDHL, our results show that the processes induced by photons in CO ice from a broad energy range are different and more complex than the sum of individual processes induced by monochromatic sources spanning the same energy range, as a result of the existence of multistate electronic transitions and discrepancy in absorption cross sections between parent molecules and products in the Ly-α and H 2 molecular emission ranges.

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